Ground Investigation – Drilling Over Water at Empress Docks, Southampton

20.03.16

REC was commissioned by ABP to carry out investigation works to determine the geo-technical parameters of Empress Docks, Southampton.

The purpose of the investigation was to confirm the presence of landwards buttresses behind the quay wall and provide information on the base and thickness of the quay wall. The buttress locations had to be facilitated as offloading was about to take place on the docks. For offloading to occur two cranes of an average loading of 32 kPa would be sited on the Quayside and therefore information is required on the construction.

It was considered necessary for the investigation, due to base and thickness of the sea wall, that works would be required to take place over water, therefore works consisted of a rotary drill at two locations taking place upon a pontoon tied to the quay wall. A further four rotary holes were advanced and installed with the emplacement of data loggers the groundwater variations in levels were recorded over a period of three weeks.

The buttress locations were identified through positive and negative obstructions of a sonic spike. Upon encountering the first positive obstruction, full delineation was ascertained by reducing the probe intervals to 1m centres both forward and backward of the encountering position, a total of 44 sonic probe holes were advanced. In order to fully and positively identify the obstruction as being the buttress a further two rotary core holes were drilled.

Laboratory analysis of the rotary cores consisted of Uniaxial Compressive Strength of Rock (UCS) within Buttress 1 and 3 which results were used by others to ascertain the capable load.

Full Health and Safety measures had to be implemented, including harnesses and life jackets worn by all site personnel near or on the water, and the pontoon was fitted with safety rails and secured to the quaysides at all time.

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